Answer: Cellulose cannot be digested and broken down by herbivorous digestive system.
Herbivores feed on plant based food. The herbivores have a digestive system which is capable of digestion of plant materials. The plants have higher starch and fibre which are the main energy source in the diet. Some of the plant materials like cellulose are hard to digest. The digestive tract of herbivores is adapted such that plant food is digested properly. The herbivorous organisms lack enzymes for the digestion of the cellulose.
The cranial capacity of Homo sapiens are responsible for their successful adaptation on earth. They have the cranial capacity of around 1400cc.
The major environmental conditions has changed but the complex human brain has helped him to sustain and understanding the nature. Humans are successful to sustain on this earth due to their complex brain.
